Hydraulic shock absorber



June 11, 1935. R. F. PEO ET AL HYDRAULIC SHOCK ABSORBER Filed May 7, 1954 4 Sheets-Sheet 1 1 74 EJWIEFE Edi OZ L7. Pea. John 6% llt'wwz.

June 11, 1935.

R. F. PEO El AL HYDRAULIC SHOCK ABSORBER Filed May '7, 1934 4 Sheets-Sheet 2 ti I. .1

June 11, .1935. R. F. PEO El AL HYDRAULIC SHOCK ABSORBER Filed May 7, 1954 4 Sheets-Sheet 3 All!!! 2611,94 2&0;

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J 1935. R. F. PEO ET AL HYDRAULIC SHOCK ABSORBER Filed May '7, 1954 4 Sheets-Shet 4' ll-II lllll Patented June 11, 1935 v i 2,004,904

2,004,904 HYDRAULIC snoox ABSORBER Ralph F. Peo and John Sullivan, Buffalo, N. Yi, assignors to Houde Engineering Corporation, Buflalo, N. Y., a. corporation oi. New York Application May 7, 1934, Serial No. 724,288

14 Claims. (01. 18889) This invention relates to hydraulic shock abpartly in sectiomshowing amodified arrangement sorbers and the object is to provide improved f r fl fi l means'formetering and controlling the flow of F gu 1315 asection 011 p a e the displaced hydraulic fluid so that the shock ure 12; and g .5 absorbing characteristics of the shock absorber Figure 14 isa section on plane I l-l4, Figwill not be interfered with by variations in temure 12. I perature of the fluid. Briefly describing-the shock absorber to which The important feature of the invention resides we have shown our inventi n ppl it in the provision of a passageway between the p ses a e hav theanmllar Wall H f e-UNITED STATES PATENT OFFICE working chambers of the shock absorber in which tending'therefrom and provided with apertured 1.0

passageway is interposed a knife edge orifice for a s l2 by m a s o which it y be secured to a a restricted flow of the fluid at a rate substantially support such as the chassis of an automotive independent of viscosity changes in the fluid, vehicle. Received within the annular wall I l is and the provision of a second passage between the a ring 3 from WhiCh diametrically pp D 1'5; working chambers for which second passage a tit on u s l4 a l4'zextend r y, t

check valve is provided for permitting free flow structure being rigid y Secured y means of P through the passagefrom the low pressure to the I 5 extending through the partition lugs and into high pressure chamber and for restricting the the base II].

passage against flow from the high pressure to An end or cover wall l6 abuts the ring and parthe low pressure chamber together with thermo'-' titionlugsand is held in place byan annular nut 20,

static means for automatically adjusting the reor collar'l'l abutting the wall and having threadstriction to compensate for variation in temperaed engagement with the outside of the annular ture of the fluid. a wall 1 l. e A cylindrical piston hub 18 extends be- Another feature of the invention resides in the tween the base I0 and wall I6; and between the provision of a: bimetallic thermostat element partition lugs I4 and I4 and has a shaft l9ex-' 25 whose end forms the check valve and is'moved tending therefrom for bearing engagement in the transversely of the passageway by the thermostat wall l6 andits bearing entension I6.

element and is provided with a slot for variable The piston hub I8 has the diametrically oppooverlap of said passageway for metering flow site vanes-20 and 20f extending therefrom and from'the high pressure chambers to the low presthese vanes together with the partition lugs di- 30v sure chambers in addition to the flow through vide thespace within the ring l3 into high presthe sharp edge orifice. sure chambers 22 and 22' and low pressure cham- The various features of our invention are inhers 23 and 23 between which the hydraulic fluid corporated in the structure shown on the drawflows when displaced by the vanes during oscil- 35. ings, in which drawings: lation of the piston structure, the shaft l9 at its Figure 1 isa plan view of a shock absorber with outer end having a lever 24 extending therefrom the endwall structure removed; whichis connected usually with the axle of the Figure 2 is a section on plane II-II of Fig automotive vehicle. ure 1; g At itsinnerend the piston hub has the cylin- Figure 3 is a section on plane III-III of Figdrical recess 25 for receiving the centering and 40 ure 2; and bearing lug 26 on the base-l 0, the space or cham- Figure 4 is a developed view of the thermostat ber 21 being left between the lug and the shaft. element; v This space is connected with the high pressure Figure 5 is a plan view of a piston vane show chambers 22' and 22"by the passages 28 and 28' 15 ing a modified flow controlling arrangement; respectively extending through the piston hub Figure 6 is a section on plane 6-6, Figure 5; wall.

'- Figure 7 'is a side view of the supporting and A bore 29 leads into the piston hub from the adjusting element for the thermostat coil in recess 25'to form a chamber which at its inner Figures 5 and 6; end is connected with the-low pressure chambers Fi 8 is a vi w m r o Fi ure 5 showing 23 and 23'by passages 30 and 30' respectively ex- 50 another modified arrangement; tending through the piston hub. Figure 9 is a section on plane 99, Figure 8; At its outer end the bore 29 is of increased di-'- Figures 10 and 11 are plan views of the ends of ameter to form a pocket 3| and an'annular shoulalves S ow modified arrangement of Parts; der 32. An abutment member 33 fits intothe ;Figure'l2 is aside View of the piston structure, pocket and rests against the. shoulderiand has tallic disc 35 is clamped against the abutment member 33 by a ring 36 which may be secured by threading into the pocket 3| or as shown may be secured in place by deflection against the outer face thereof of the metal at the outer edge 'of the pocket 3|, as indicated at 31. The disc 35 has the opening 38 therethrough,forrning-. a sharp of the coil so that the fluid may readily flow and be metered and resisted only by the orifice 4| which is large as compared to the size of the orifice 38. The plate or wing 50 extending from the thermostat coil thus acts as a check valve.

As the temperature changes, the thermostat coil will tend to wind or unwind and thereby cause shiftpfthe valve plate 50 onthe. seat bushing 42 in a directiontiansversely of the passageway 39. We have shown aslot cut in the valve wing piston structure oscillates, the displaced hydrau ill inwardly from one side edge thereof, this slot lic fluid will flow back and forth through this sharp edge orifice which will meterthe 'flout and will tend to compensate forvariations ii -viscosity. V e

tendtounwind,v and to thereby shift the valve "f fo'r. greater overlap of the slot 5| with the passagecaused mostly by variatior'iin'iemperatureiof the fluid so as to maintain the resistance' te such constant. p

The knife edge orifice will effect practical and efficient compensation during a normalrange of f to lessen the degree of overlap.

temperature variation but frequentlyth e shock absorberwill be subjected to abnormal: tempera-. tures and provision should therefore bemade' forassisting" the orifice during -such abnormal temperature conditions. Furthermore it is usual to' provide for less resistance-arid easier-flow ofthe hydraulic fluid during the bump stroke of the piston structure, that is, when the vehicle. springs are flexed, as when the vehiclebody' and axle' approach each other. W'e provide simple means for-relief of resistance 'during 'the bump stroke and for 'assisting the "sharp edgef orifice 39 111 properly metering the flow and compensating for temperature variations, particularlyduring 'the rebound-strokes of thepi ston structure, thatfis' whenthe vehiclesprings rebound.

In the' arrangement-shown in Figures 1-'4, the pistonvaheZil-has an auxiliary passage 39 extending transversely therethrough into which projects'the' annular flange '49 forming themetering port or orifice 4|. The upper end of the" passageway 39 communicateswith the highpressure chamber fl and the lower end communicates with the low pressure chamber 235;: and in "the upper end is inserted a'bushing 42 'which seats against the flange 40 and projects a slight disthermostat element which, as shown; maybe in the form of a spiral coil of bimetal. The inner end of the coil 'en'gagesin' the longitudinal slot 45 in the shank of a bolt which extends through the'bottom of the pocket 43'iwith its head abut ting the under face "of the vane 20'. A washer 41 is interposed between the inner portionof the coil and'the bottom of ithe pocket 43 and'another washer 48 is interposed between the inner portion' of the coil and 'a nut 49 for the boltso that thecoil maybe clamped and held at its inner end, leaving'the outer portion of 'the'coil free for winding or' unwinding in response to' temperature change v l The outer end of the coilband is-deflected outwardly at right angles to the coil'axis to provide the plate or wing 50 which overlies the outer end of the bushing 4Z'to a'ctas a valve for controlling the flow; through the' passageway 39. The body of the coil acts-as a'spring! tending to hold the valve'plate seated againstithe outer end of the bushing 42 so asto' cut off 'fiow'th'roughthe pas-- sage '39: during rebound stroke of the piston structure. During the bump stroke. the pressure of the fiuidflow through thepassageway 39 will lift. the valve plate against athe spring: resistance being preferably of varying width, being V-shaped as; slmwnofil-h'farrangement is such that with decreasing temperature the thermostat coil will my 39, "and with increasing temperature the 'thermostat' coil will tend to wind up and cause shift of the valve wing in the opposite direction -Byxloosening the nut 149 thelbolt46 mayhe turned f or propersetting :of. the valve' for normal temperature operation; The slot orifice 5| maybe entirely closed or .inlpartial overlap with "theipassageway; 39 during normal. temperature, depending upon the operation of the orifice 38. t'lhe thermostat control valve willthen cooperate with the orifice 381to' meter the fiow fromthe high pressure chambers to the low pressure chambers and to compensate for variation in temperature. The flowxfrom the low;pressure' chamberstotthe high pressure chambers will bet-mainly through thepassageway 39 under meteringacontrol by the orifice 4 I.--, only part of .the fluid flow being through theorifice38. The flow, from the low, pressure chambers to the high pressure chambers, occurs when the piston structure rotates in clockwise direction, Figure 1; for the bump strokes. The valve 50zwi11 readily yieldgto such aflowaso' that the passageway II will be practically unobstructed. except 'for'oriflce The flow from the high pressure chambers to the low pressure chambersoccurs during the rebound of, the :vehiclesprings and movement in counterclockwise direction of .the piston structure; the pressure forcing the .valve ifl againstxits seat. The flow will be from the high pressure chambers through the ports: 28 and =28; into the'space, 21 and then-through the sharp edge orifice into the chamber 29 and from "there toqtheports=30 and 30' into the low pressure chambers. -While. the

notch 5| :in the valve'iflgisyin; overlap with the passageway someof the fluid will flow from the high pressure chambers into: the low pressure chambers through theexposed notch. The, adjustment of the thermostat maybe such-that the orifice 5 I will be closed during normal temperature and will be opened only when the temperature decreases beyond avnormal range, or, the prince 5| may be open at all times but the area of the opening automaticallycontrolled by the thermo-' stat as the temperature varies. When thetemperature increases, the available passage through the orifice 54 will" be decreased and when the temperature decreases the available size of the orifice will increase so that change inviscosityresulting from change in temperature will be compensated for and the shock absorbing characteristicsof. the shock absorber maintained throughout a wide range of'temperature andviscosity variations' i Y The thermostat coil is fully protected within the pocket 43 and besides functioning thermostatically to'shift the valve forsetting of the orifice 5| it also serves the function of a spring tending to resist deflection of the valve during flow from the low pressure chambers to the high pressure chambers and to keep the valve seated. This combined thermostat and valve structure can be very readily and economically manufactured and installed.

Figures 5, 6 and '7 show a modified arrangement. Here a bushing 52 extends entirely through the transverse passageway 53 shown in the piston vane 20. high pressure chamber, has a valve seating flange 54 engaging the adjacent face of the vane, and the other end of the bushing is deflected over against the opposite face of the vane as indicated at 55 in order that the bushing may be rigidly held in the passage 53. Intermediate its ends the bushing has the cross wall 58 with a port 5'1 therethrough forming a metering orifice for fiow from the low pressure to the high pressure side of the vane, this orifice being offset to one side of the center of the cross wall 56 for a purpose to be specified later.

'Adjacent to the bushing the vane 20 has a pocket 58 for receiving the bimetal thermostat coil 59 whose inner end engages in the slot 69 in the cylindrical shank 6! of a bolt 62 which extends through the vane to receive the nut 63 between which nut and the head the vane is clamped to thus secure the head and thermostat coil in adjusted position. The bolt has the reduced end or neck 64, which, after application of the thermostatcoil to the bolt head, receives a collar 65 so that the coil end will be held against axial movement between the bottom of the slot 60 and the collar.

The outer end of the thermostat coil is defiected to form the valve plate 66 which is normally held by the spring action of the coil against the bearing flange 54 of thebushing 52 and which has the V-shaped orifice notch t1 adapted for variable overlap with the bore of the bushing 52 as the valve plate 86 is shifted laterally by the winding or unwinding of the thermostat coil in response, to temperature change. Flow from the low pressure to the high pressure side of the vane raises the valve plate against the spring resistance of the coil for comparatively free flow of the fiuid under the restriction only of the comparatively large orifice 57. The flow from the high pressure to the low pressure side of the vane is checked by the seating of the valve plate and is restricted to the end of the orifice notch which overlaps the bore of the bushing 52. The space within the bushing between the valve plate and the bushing wall containing the orifice 51 forms a relief or expansion chamber 68 in which the high pressure flow through the restricted orifice 61 mayidissipate some of its velocity before the fiuidpasses through the offset orifice 5?, the arrangement eliminating the so-called 'swishing noise. r

In the arrangement of Figures 5 and 6, and also in the arrangement of Figures 2 and 3 the width of the valve plate may be the same as the diameter of the seating flange on the respective bushing, and the orifice notch is located so that when the thermostat coil is adjusted for normal temperature setting the valve plate side edges will register with the opposite sides of thebushing. After such setting the degree of overlap of the orifice slot will be that for volume of flow through the orifice at normal temperature, say 70 F.

In the modified arrangement of Figures 8 and 9 the passageway 69through the piston vane has The bushing, at its end exposed to the.

the cross wall I0 intermediate its ends provided with the orifice 1| offset from ,the center of the passageway, and in the high pressure end of the passageway is inserted the bushing 12 with the seating flange 13. In the arrangement shown for the thermostat coil, no recess is provided therefor, the coil being mounted with its inner end in the circumferential channel 14' in the head 14 of the bolt 15 extending through the vane and locked in adjusted position by a nut 15. The bolt head has the diametral slot 98 into which the inner end of the coil I00 extends, the coil being readily expansible to be slipped over the outer end of the head and into the channel 14'. The outer end of the coil is deflected to form a valve plate 16 which has the orifice notch 11 adapted for variable overlap with the bore through the bushing 12 so as to meter the flow from the high pressure to the low pressure side of the piston structure. To facilitate adjustment of the thermostat the, orifice notch 11 is so arranged adjacent to one side edge of the valve plate that when the opposite edge alines with the edge of the seating flange 13 the overlap of the orifice will be that for flow control at normal temperature.

In the arrangement shown in Figure 10 a restricted orifice is provided in the valve plate 18 in addition to the notch orifice 79, this orifice 80 communicating at all times with the bore in bushing 8|. The orifice notch will then, by its varying overlap with the bushing bore during change in temperature,-increase or reduce the total available flow passage from the high pressure to the lowpressure side.

In the arrangement of Figure 11 thevalve plate 82 has the restricted orifice 83 therethrough which may always be in communication with the bore through the seat bushing 84 while a row or cluster of other orifices 85 may be consecutively brought into registration with the bushing bore as the temperature-decreases so as to increase the available flow passage with decreasing temperature. H H v I These orifices may be knife edged in order to meter the fluid flow independently of viscosity changes.

In Figures 12, 13 and 14 a modified arrangement is shown for the flow of fluid between the 1 high pressure and low pressure chambers of the shock absorber. Like in the arrangement of Figures land .2 a disc 3 5 providing the knife edge orifice 38 may be. interposed between the chambers 21 and 29, with the passages 28 and 28 leading from chamber 21 to the high pressure working chambers and passages 30 and 30' leading from chamber 29 to the low pressure working chamber of the shock absorber. However, instead of having an auxiliary passage exceiving the bushing 88 whose bore 89 connects the high pressure side of the vane with the passage 88, the outer end of the bushing having the seating flange 90 for'thevalve plate 9| at the outer end of the theremostat coil 92 which exten s partly into a pocket 93 formed in the vane adjacent to the bushing, the coilbeing anchored at its inner end 'to the' head of a bolt 94 which is secured' by a'nut 95. The valve plate has the orifice notch BB for variable overlap with the bushing bore as the temperature changes.

During the low pressure stroke ofthe shock absorber most of the displaced fluid flows through the passages 30 and 30 into the chamber 29'and from there through the passage 86 and through the bushingbore 89 past the valve 9| and into the high pressure workingchamber, part of the fluid fiowing from the chamber 29 through the orifice 38 and through the passages 28 and 28' to the high pressure working chambers. During the high pressure stroke or rebound stroke of the shock absorber the valve plate 9| is forced against its seat, part of the displaced fluid then flowing I through 28 and 28, through the orifice 38 to chamber 29 and from there through passages 30 and 30 into the low pressure working chambers,

the balance of the fluid flowing through the retricted thermostat controlled orifice 96 into the passage 86 and from there to 'thechamber 29 and through passages 30, 30 to the low pressureworking chamber.

For some-kinds of service the thermostat controlled valve could be relied upon solely for controlling the fluid flow. "In that case, in the structure shown, there wouldbe a'solid wall between the chambersl'l and 29, or, a solid continuous disc could loe substituted for the orificed disc 35. It 'is also evident that the thermostat controlled valve structure could be applied toone of the partition'lugs l4, l4 instead of to one of the piston vanes. 1

We have shown practical and efficient embodiments ofthe various features of our invention but we'donot desire'to be limited to the exact construction, arrangement and operation shown and described as changes and modifications may be madewi-thout departingfrom the scope of the invention. Y a a 'We claim as followst I. In a hydraulic shock absorber, the combinamosta-t element having a portion thereof formed to provide a valve extending transversely of said passageway, said valve portion having a restricted port arranged for variable exposure to said passage as said thermostat element responds to temperature changes. 2; In a-hydraulicshock absorber, the combination of a housing forming a chamber for hydraulic fluid, a piston structure operable within said chamber to displace the'fluid therein, a passageway for the flow of hydraulicfluid from one side of the piston structure to theother, a thermostat element-in the form of a bimetal coil, one end of said coil being shaped to form a valve for closing said passage against unrestricted flow and having a port arranged for varying exposureto said passage'as said coil' winds orunwin'd in response to temperature changes.

3. In'a hydraulic shock absorber, the combination of a housing forming achamber for hydraulic fluid; a piston structure operable within said chamber .to displace the fluid therein, a passageway for the flow of hydraulic fluid from one side of the piston structure to the other, a thermostat elementjtn the form of a bimet'al band anchored at one end and having; its outer end shaped to form avalve plate .for normally closingsaid passageway against unrestricted flow therethrough in one direction, said thermostate element being yieldable for movement of said valve plate away from said passageway in the direction of the axis thereof for unrestricted flow through said passageway in the opposite direction, said thermostat element being arranged to move said valve in the direction at right angles to the axis of saidv passageway in response to temperature changes, and I a restricted port through said valve plate arranged for variable exposure to said passageway as said valve plate is moved by said thermostat element in response to temperature change.

4. In a hydraulic shock absorber, the combination of a housing forming a chamber for hydraulic fluid, a piston structure operable within said chamber to displace the fluid therein, a passageway for the flow of hydraulic fluid from one side of the piston structure to the other,.a thermostat elementin the form of a bimetal band anchored at its inner end with its outer end extending across and normally seated over one endof said passageway to close said passageway against unrestricted fluid flow-therethrough in one direction, said thermostat-element being yieldable to open said passageway to unrestricted flow therethrough in the opposite direction, the outer end of said thermostat element having a slot and said thermostat element being arranged to shift said outer end for variable overlap'of said slot with said passageway as said element responds to temperature changes whereby to correspondingly restrict the flow through said passageway in the first mentioned direction. I,

5. In a hydraulic shock absorber, the combination of a housing, a shaft journalled in said housing,'a piston on said shaft and traversing the space between said shaft and housing, a stationary element in said housing and traversing the space between said shaft and housing, said piston and stationary element forming a pair of working compartments, a passage connecting said compartments, a valve for said passage machined to provide a port, a separaterecess at one side of said passage, and a thermostat element within said recess and connected with said valve and adapted to movesaid valve for setting of its port relative to said passage whereby to regulate the flow of fluidthrough said passage.

6. In a hydraulic shock absorber, the combination of a housing, a stationary element and a movable'element in said housing dividing said housing into working compartments for containing hydraulic fluid, a passageway through one of through said passageway'in the opposite direction I way, a thermostat element in the form of a bimetal coil within said recess and having its outer end extending against the adjacent side 'of said element andv over the corresponding'end of said passageway to form a valve, said valve being shiftable laterally. by the winding or unwinding movement'ofsa-id thermostat coil in response to temperature changes for controlling the flow through said passageway.

8. In a hydraulic shock absorber, the combination of a housing, a movable element and a stationary element within said housing dividing the space therein into working compartments for containing hydraulic fluid, one of said elements having a passageway therethrough from one compartment to the other and a recess adjacent to said passageway, a thermostat element in the form of a bimetal coil within said recess and having its inner end anchored to said element, the outer end of said coil being deflected to form a valve plate extending across the adjacent end of said passageway, said thermostat coil acting as a springtending to hold said valve plate against the respective end of said passageway and to yield for movement of said valve in the direction of the axis of said passageway for unrestricted flow of fluid from the opposite end of said passageway, said valve being shiftable transversely of said passageway by the winding or unwinding movement of said coil in response to temperature changes for variable restricted exposure of said passageway for flow therethrough in the opposite direction.

9. In a hydraulic shock absorber,v the combination of a housing forming a chamber for hydraulic fluid, a piston structure operable within said chamber to displace the fluid therein, means forming a passageway for the flow of hydraulic fluid from one side of the piston structure to the other and a restricted sharp edge orifice interposed in said passageway, means providing an auxiliary passageway for the flow of fluid from one side of the piston structure to the other and a recess adjacent to said auxiliary passageway, a thermostat element in the form of abimetal coil within said recess and having its outer end projected across the adjacent end of said auxiliary passageway to form a valve, said coil serving as a spring tending to seat said valve against the passageway end to seal said passageway against unrestricted flow therethrough from said end but permitting said valve to unseat for unrestricted flow in the opposite direction through said auxiliary passageway, said thermostat coil when winding or unwinding in response to temperature change causing lateral shift of said valve, and a restricted port through said valve arranged for variable overlap of said auxiliary passageway during such shift of the valve to correspondingly control the restricted flow through said auxiliary passageway.

10. In a hydraulic shock absorber, the combination of a housing forming high and low pressure chambers for hydraulic fluid, a piston structure operable to displace said fluid from one chamber to the other, means providing a passageway for flow of fluid between said chambers and a sharp edge restricted orifice interposed in said passageway, means providing an auxiliary passageway for the flow of fluid between said chambers, a thermostat element in the form of a bimetal band anchored at its inner end adjacent to the high pressure chamber end of said auxiliary passageway and having its outer end extending across said passageway end to form a valve, said thermostat element tending to hold said valve seated over said end of said-auxiliary passageway to close said' passageway against unrestricted flowfrom the high 'pres'sure to the low pressure chambers but ibein'g yieldable to-permit lifting of said va1ve"forunrestricted flow throughsaid auxiliary passageway from the" low pressure to the/high pressurechambersjsaid thermostat element being arranged to shift said valve laterally in response to temperature changes for variable restricted flow through said auxiliary passageway from the high pressure to the low pressure chambers for cooperation with said knife edge orifice to keep the flow from the high pressure to the low pressure chambers independent of temperature and viscosity change.

11. In a hydraulic shock absorber, the combination of ahousing, a stationary member in said housing and a movable member therein for displacing hydraulic fluid, there being a passageway through one of said elements having a cross wall intermediate its ends provided with an orifice at one side of the wall center, a thermostat element in the form of a bimetal coil, one end of said coil being shaped to form a valve extending across one end of said passageway and having a port arranged for varying exposure to said passageway as said coil winds or unwinds in response to temperature changes, said valve closing said passageway against flow therethrough in one direction except through said valve port, said thermostat coil permitting yield of said valve for freer flow through said passageway in the opposite direction, the space between said valve and said cross wall forming an expansion chamber for dissipat ing the velocity energy of the fluid flowing through said valve port before said fluid reaches the port in said cross wall.

12. In a hydraulic shock absorber, the combination of a housing forming a chamber for hydraulic fluid, a piston shaft extending into said housing and having a vane thereon for displacing the hydraulic fluid when the shaft is oscillated, there being a passageway extending through said vane and said shaft and terminating in said housing at one side of said vane, said vane having a port extending therethrough from the other side thereof and to the passageway therein, a thermostat in the form of a coil mounted on said Vane and having its outer end shaped to form a valve plate extending over the outer end of said port, said valve plate having an orifice slot therein arranged for varying exposure to said port as said coil winds or unwinds in response to temperature changes.

13. In a hydraulic shock absorber, the combination of a housing forming a chamber for hydraulic fluid, a piston structure operable within said chamber to displace the fluid therein, a passageway for the flow of hydraulic fluid from one side of the piston structure to the other, a thermostat element having a portion thereof formed to provide a valve extending transversely of said passageway and having a metering slot therethrough of varying width, said thermostat element being arranged to function mechanically as a spring tending to move said valve in one direction to hold it over one end of said passageway and to function thermostatically to shift said Valve in a direction at right angles to said first -mentioned direction for variable overlap of said passageway by said valve metering slot in accordance with change in temperature of the fluid.

14. In a hydraulic shock absorber, the combi-,

nation of a housing forming a chamber for hyapes-,9

of knife edge orifices therethrough one orimore of which is exposed to said passageway as said thermostat responds to the fluid.

change in temperature 01 RALPH F. PEO. JOHN SULLIVAN 

